1. Field of the Invention
This invention relates to radiation sensitive materials, and particularly photographic materials, their preparation, their use and polymeric compositions useful therein. In particular, this invention relates to the preparation and use of sulfonated anionic microgel latices to form electrically conductive or antistatic layers in radiation sensitive materials. These latices are clear and colorless and have an average diameter particle size of less than 1 micron.
2. Description of the Prior Art
Sulfonated styrene-containing resins are quite well known as useful in many connections. Several references disclosing various utilities include U.S. Pat. Nos. 2,533,210, issued Dec. 12, 1950 and 2,718,514, issued Sept. 20, 1955 which relate to the sulfonation of polystyrenes with a complex of sulfur trioxide and bis-(beta-chlorethyl) ether for use as dispersing agents, thickening agents and the like; U.S. Pat. No. 2,616,917, issued Nov. 4, 1952 which relates to polymers containing alkyl styrene sulfonate moieties; U.S. Pat. No. 2,837,500, issued June 3, 1958 which discloses the use of such resins as soil conditioners and dyeable fibers; U.S. Pat No. 2,909,508, issued Oct. 20, 1959 which relates to polymers of acrylamides and sulfonated styrenes useful as flocculants; U.S. Pat. No. 3,072,618, issued Jan. 8, 1963 which relates to sulfonation with sulfur trioxide-phosphate complexes; and U.S. Pat. No. 3,917,574, issued Nov. 4, 1975 which discloses a water-soluble sulfonated polystyrene-containing polyelectrolyte.
It is also known that polyvinyl aromatic monomers such as divinyl benzene, can be copolymerized with other aromatic monomers, such as styrene, to give crosslinked resins which are used advantageously in various ways as disclosed, for example, in U.S. Pat. No. 3,043,817, issued July 10, 1962; U.S. Pat. No. 3,549,562, issued Dec. 22, 1970; British specification No. 1,339,988, published Dec. 5, 1973; and West German Pat. No. 2,258,298.
Polymeric dispersions have been sought for some time for a variety of uses which have specific polymer particle sizes. Generally, suspension polymerization techniques, whether batch or continuous, have yielded particle sizes greater than 50 microns, but sometimes as small as 2 microns, as noted in U.S. Pat. No. 2,694,700, issued Nov. 16, 1954; U.S. Pat. No. 2,712,536, issued July 5, 1955; U.S. Pat. No. 3,631,014, issued Dec. 28, 1971; and U.S. Pat. No. 3,649,610, issued Mar. 14, 1972. Emulsion polymerization typically yields polymers having smaller particle sizes. U.S. Pat. No. 3,232,899 discloses a latex of a styrene-containing polymer having 0.05 to 0.3 micron particle sizes, which when dried forms a continuous film. Similar emulsions are described in U.S. Pat. No. 3,513,120, issued May 19, 1970. Netherlands Pat. No. 68,08638 relates to styrene-containing xerographic toner particles having particle sizes less than 20 microns.
Sulfonated polystyrenes have been mixed with ammonium fluoride and gelatin and used in layers of photographic elements to improve viscosity and conductivity of the layers, as disclosed in U.S. Pat. No. 3,861,924, issued Jan. 21, 1975. No crosslinked sulfonated copolymers containing polyvinyl aromatic moieties are disclosed, however.
U.S. Pat. No. 3,574,682, issued Apr. 13, 1971 relates to electrostatographic recording materials comprising a conductive processing agent which comprises polyvinyl benzene sulfonic acid or a salt thereof.
U.S. Pat. No. 2,678,306, issued May 11, 1954 relates to sulfonated, crosslinked terpolymers of styrene, a polyvinyl aromatic and another monomer containing pendant carboxyl groups which terpolymers are useful as cation exchange resins. The sulfonation was carried out with chlorosulfuric acid. The particle size of the resins, like that for all ion exchange resins, is considerably greater than 1 micron, and typically greater than 5.0 microns.
Both cationic and anionic resins are known to be useful as conductive membranes, as disclosed in U.S. Pat. Nos. 2,731,411, issued Jan. 17, 1956 and 3,887,499, issued June 3, 1975. Sulfonated, crosslinked ion exchange resins are also quite well known in the art, as disclosed in U.S. Pat. Nos. 3,792,029, issued Feb. 12, 1974 and 3,870,663, issued March 11, 1975; and West German Pat. Nos. 1,919,382 and 2,015,206. Generally, sulfonated ion exchange resins, however, are made by suspension polymerization, resulting in average particle sizes significantly greater than 1 micron. Simply ball milling large particulate resins to produce smaller particles is impractical. To break particles down to less than 1 micron in size would require weeks of high energy milling with the attendant high energy costs and time expenditure. Further, since milling is often carried out in oily hydrocarbon solvents, the milled resins may be adversely affected or degraded in properties, such as undesired softening or reduction of storability. These adverse effects have been noted for other (non-sulfonated) resins and photographic materials, as disclosed in U.S. Pat. Nos. 3,418,127, issued Dec. 24, 1968 and 3,518,088, issued June 30, 1970. Moreover, milled resins must be isolated from the milling solvents and any impurities collected from the milling process before they can be used, thereby necessitating further manufacturing costs and time. It is not expected that ion exchange resins, if they could be ball milled to 1 micron particles would be useful as antistatic agents after subjection to the high energy milling process and organic milling solvents. Yet, larger particles would not give the clear and colorless films desired when coated with binders.
It is known that radiation sensitive materials and particularly photographic materials, have a tendency to accumulate static electrical charges during manufacture, handling and use. The static discharges cause irregular fog patterns in radiation sensitive layers or in photographic emulsions present therein. The static charges are also undesirable because dirt which the charges attract to the charged layers, causes repellancy spots, desensitization, fog and physical defects.
The generation of a static charge is a dynamic phenomenon which is affected by the rate of contact electrification of the charged layer by friction and the conductivity of the sheet (surface and internal) which controls the rate of dissipation of the charge. To avoid static charge the dissipation rate must be greater than the electrification rate. This value is determined herein by measuring surface conductivity in terms of surface resistivity at specific conditions of temperature and humidity, namely at 70.degree. F. (24.degree. C.) and 50% relative humidity, between two electrode plates and calculating the surface resistivity according to the formula: ##EQU1## Further discussion of resistivity is found in U.S. Pat. Nos. 2,801,181, issued July 30, 1957 and 3,525,621, issued Aug. 25, 1970.
Antistatic layers are discussed in U.S. Pat. Nos. 3,376,277, issued Apr. 2, 1968 and 3,857,729, issued Dec. 31, 1974; Belgian Pat. No. 764,085; and British specification No. 1,217,184, published Dec. 31, 1970. Japanese Pat. No. 4722474 relates to water-soluble sulfonated styrene-containing copolymers which are useful in antistatic compositions. The polymers are sulfonated with sulfur trioxide adducted with dioxane. U.S. Pat. No. 3,681,070 relates to the sulfonation of uncrosslinked styrene-containing polymers with sulfur trioxide. The resulting polymers are used as antistatic coatings for sheet materials. U.S. Pat. No. 3,791,831, issued Feb. 12, 1974 relates to a mixture of polymers of, or a graft copolymer of, monomers having sulfo groups and monomers having carboxyl groups. The polymers are useful in antistatic layers although essentially water-soluble and uncrosslinked.
Hence, there is a need in the art for antistatic agents which can be used in radiation sensitive materials, and particularly photographic materials, without adverse sensitometric effects, which will not migrate throughout the various layers of such materials during processing, and which are clear and colorless. Further, there is a need for water-insoluble, but water-dispersible, crosslinked, sulfonated polymers which already have particle sizes below one micron assuring clear and colorless coatings. Such polymers are not readily produced by the mechanical breaking down of larger-sized polymer particles.